Late magmatic controls on the origin of schorlitic and foititic tourmalines from late-Variscan peraluminous granites of the Arbus pluton (SW Sardinia, Italy): Crystal-chemical study and petrological constraints

Petrogenetic controls on the origin of tourmalinite veins from Mandrolisai igneous massif (central Sardinia, Italy): Insights from tourmaline crystal chemistry

“…More specifically, according to Henry and Dutrow (1996) and Ertl et al (2012), the relevant number of X-site vacancies and the absence of Al at the T site indicate a formation temperature for BUP4 below 450 °C. All these findings converge to a crystallization scenario for the Mandrolisai tourmalines in the range 650-400 °C, consistent with the temperature limits previously obtained for tourmalines of the Arbus pluton (Bosi et al, 2018). The parallel though not overlapping trends observed in Figure 9 may be explained in terms of the peraluminous character of the Arbus pluton (ASI < 1.16) with respect to the metaluminous character of Mandrolisai.…”

“…Tourmaline growth recorded the latestages of consolidation of a single magma batch, whose crystallization locally led to residual concentration of B in the melt. Similarly to what recently described for the Arbus pluton (Bosi et al, 2018), in layered aplite/pegmatite rocks the enrichment of B promoted the crystallization of tourmaline + quartz at the cores of pegmatitic bodies as a response of melt/hydrous fluid immiscibility processes (Hulsbosch et al, 2017;2018). The early generation of tourmaline (b-and c-type) was followed by emplacement of tourmalinite veins, made of fine-grained tourmaline (a-…”

“…In the Late-Variscan magmatism of Sardinia, tourmaline is documented not only in peraluminous (ASI > 1) but also in metaluminous (ASI < 1) intrusions, mainly occurring in pegmatites within granodiorites and granites belonging to the old magmatic peak (OMP sensu Conte et al, 2017). Detailed information is only available for the weakly peraluminous Arbus igneous complex (southwestern Sardinia) in which tourmaline crystallization has been related to late-stage evolution of cordierite-bearing granitic melts at shallow crustal levels (Bosi et al, 2018). An example of tourmaline-bearing rocks related to metaluminous granodioritic magmas is offered by the Mandrolisai igneous massif (central Sardinia).…”

“…Assignment of bands to specific atomic arrangements in the (OH)-region may be just tentatively done because the relation between occupants and band positions is very complex (Hawthorne, 2016). Based on the studies of Bosi et al (2015bBosi et al ( , 2018, and Watenphul et al (2016), the main FTIR bands of the studied tourmaline can be considered to be related to the following atomic arrangements:…”

“…9). At the scale of the Sardinia batholith, comparisons may be made between the Mandrolisai massif and the Arbus igneous complex, both emplaced at a shallow structural level (Bosi et al, 2018). Tourmalines from Mandrolisai and Arbus show similar schorlitic-foititic evolutionary trends (Fig.…”